Spotter-tracer projectile



Dec. 19, 1961 T. STEVENSON ETAL 3,013,495

SPOTTER-TRACER PROJECTILE Filed July 10, 1959 INVENTORS, THOMAS STEVENSON WINSTON WCAVELL JAMES J. CAVEN RM Qd. Q4 W ATTORNEYS:

H 3,013,495 Patented Dec. 19, 1961 3,013,495 SPOTTER-TRACER PROJECTILE Thomas Stevenson, Huntingdon Valley, and Winston W.

Cavell and James J. Caven, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of the Army Filed July 10, 1959, S61. No. 826,378

3 Claims. ((31. 102-59) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention is a continuation-impart of our co-pending patent application, Serial No. 769,046, filed October 22, 1958, and abandoned after filing the present applica tion, relates to projectiles used for spotting and estimating accuracy of fire to increase probability of first round hit and particularly to projectiles where sensitivity and rapidity of function are essential.

This invention relates to the use of accuracy of the estimators in the form of small caliber projectiles designed to match closely the trajectory of the major caliber projectile, and fired from a rifle attached to the major caliber weapon. In order to obtain the best estimation of target miss distance the projectile must function quickly on any terrain as well as the target, and thereafter yield a display of flash and smoke which can be seen at the gun, but which will not obscure the target. The best available incendiary projectiles would not function quickly enough to prevent their being buried in soft earth before ignition of the incendiary. If made sensitive enough to function on soft earth or sand, the projectiles become unsafe to handle, as they would detonate if dropped. Fuzed projectiles were too costly, and did not function on the desired terrain conditions.

Therefore, an object of this invention is to make avail- I able a projectile which will trace over the entire elfective range of the weapon and then function instantaneously on all terrain with the desired display results; be safe to handle; and yet be inexpensive to manufacture.

In accordance with the present invention more nearly instantaneous function is achieved by employing a unique nose assembly having no moving parts, and arranged so that the bullet will function at substantially all angles of impact, on substantially all types of terrain. This is accomplished by having an impact sensitive primer in front of an incendiary mixture, the combination surrounded by an aluminum container, all inside an unconventional soft metal jacket. The primer is assembled in the incendiary container so as to allow an air gap between the forward end of the primer and theinner surface of the incendiary container. Sensitivity is achieved by having a hole in the nose of the jacket so that the forward portion of the incendiary container is open to air pressure. Sensitivity is controlled by proper selection of hole size, thickness of the nose section of bullet jacket, thickness of the incendiary container, and space between the impact sensitive primer and the incendiary container. Safety in handling is achieved by controlling the distance from the jacket nose to the incendiary container, such that when the projectile is dropped from 50 feet onto concrete or a steel plate the nose will crush sufiiciently to absorb the impact without striking the primer. The projectile is believed to function due to crush-up of the incendiary container or due to entrapment and compres sion of air, earth, or other material at the open nose, when the bullet strikes a target or the earth causing the incendiary container to collapse and impinge upon the primer, or the incendiary container is not broken, it compresses the gas between itself and the primer thereby detonating the primer.

The novel features of the present invention, as well as additional advantages thereof, will be better understood from the following detailed description, when read in connection with the accompanying drawing in which:

FIG. 1 is a cross-sectional view of the bullet assembly;

and

FIG. 2 is an enlarged view of the nose section of the bullet. I

Referring more particularly to the drawings, there is shown in FIG. 1 the preferred embodiment of the new spotter bullet, as employed in the cal. 50 spotter-tracer, wherein a soft metal, such as gilding metal jacket 1, encloses a traced material 3, except for a perforation shown at the rear, such tracer material 3 being carried in a usual container 2 and in front of which is a slug of metal 4 of suitable density and length to adjust the physical con stants i.e., weight and center of gravity, of the bullet so that it can match closely the trajectory of the major caliber ammunition. In the caliber 50 spotter-tracer, a lead antimony slug is used. The slug may be held in place by any suitable means. In the preferred embodiment, knurl ing is used which also operates as a crimping groove for the cartridge case. The knurling'prevents rotation of the projectile in the case after crimping.

The incendiary container 5 may be made of any suitable light material such as aluminum or plastic, and having the same outside configuration as the inner surface of the jacket 1. The preferred embodiment employs an aluminum container 5. An impact sensitive primer 6 has an external configuration such that when it is assembled in the container an air gap at is achieved between the front of the primer and the inside nose portion of the container 5. The forward shape of the primer has substantiallythe same shape as theinside of the incendiary container so that substantially the same sensitivity is achieved over a wide variation of impact angles. For drop safety on concrete or a steel plate after dropping fifty feet -on its nose, the distance L is adjusted such that the jacket 1 will crush but not suificiently to cause the incendiary container 5 to impinge the primer. After the primer 6 is inserted into the container 5, incendiary mix 7 is loaded behind it. The preferred embodiment uses a mixture of I 50% red phosphorous and 50% barium nitrate, by weight.

This mix yields a flash followed by smoke that can readily be seen at 2,000 yards. This mix may be any suitable incendiary composition capable of yielding a display consisting of flash and smoke which is visible at the maximum range of the major caliber weapon, but which .does not obscure the target. T Still another advantage of this design is that it lends itself to safe loading procedures since the explosives components can be loaded separately. 1' 5 7 FIGURE 2 shows the critical points of the nose assembly. In order to achieve the desired sensitivity the jacket 1 must have a perforation in its nose, the "size. of which is closely controlled. Proper selection of ,hole size D; distance L to the container; container material and thickness t; and gap between the primer and incendiary container, must be made such that sensitivity is obtained, while at the same time having sufiicient jacket material in front of the container to cushion the impact if the entire cartridge is dropped accidentally on its nose and. also suflicient to pass the 50 foot drop safety test.

The portion of the jacket in front of the incendiary must be very closely controlled dimensionally so that the jacket tapers to an extremely thin and sharp edge. This construction has been found to produce the following takes place is not sufficient to impinge the incendiary container;

(b) When the projectile is fired and sustains graze impact, the crush-up of one side of the jacket will be sufficient to transmit the force through the incendiary container to crush the primer body and detonate the charge;

When the projectile strikes wet earth, sand, gravel, etc., the material scooped-up by the nose portion of the jacket supplies suflicient force to either crush the incendiary container (and thus produce detonation) or to produce a compressive force on the gas in gap at to detonate the primer.

It is to be noted that this unique nose assembly has been designed with exactly the necessary degree of weakness so that it produces a high degree of uniformity of function and yet is long enough to absorb the energy of impact when the projectile is subjected to a 50-foot drop test. It is also to be noted that the exact dimensions of the forward portion of the jacket cannot easily or accurately be calculated but must be arrived at by trial and error, being based on the size of the projectile, materials utilized, types of primers, etc.

Observation type projectiles were first used during World War II by the Germans, but they were relatively ineffective, due to the fact that they employed a detonator actuated by a firing pin. They required a sharp stab on the detonator, and, when the bullet impacted soft earth, a cushioned impact resulted which lacked the sharpness required thereby resulting in a failure to function. If made more sensitive to the firing pin, they would function if dropped. Also, due to the position of the firing pin, the projectiles were not sensitive upon graze impact.

In the caliber 50 spotter-tracer, an impact sensitive primer is the important detonating means. Aluminum is used for the incendiary container having a wall thickness at the nose of about .012 inch constituting a diaphragm, although any suitable material whose strength and thickness can be closely controlled, may be substituted. The slug is lead-antimony, but any suitable material may be used for weight and center of gravity adjustment. The longitudinally and forwardly extending jacket has a hole diameter of about .160 inch in its nose and tapers to a thin, sharp edge. The tracer 3 comprises three mixtures of burning rates varying from very fast for the igniting section to'much slower for the innermost composition, such that the entire tracer will burn over a minimum range of about 2,000 yards.

From the foregoing description, it will become apparent to those skilled in the art that the present invention provides a combination spotter-tracer bullet which will give visible trace for a minimum of 2,000 yards when fired at a velocity of about 1700 f.p.s. impact sensitivitly on substantially all terrains and a range of impact angles, be safe tohandle, inexpensive to manufacture and assemble, and considered to be such an advance in the art that the Government has seen fit to use this bullet as the basis for establishing a new series of projectiles. The projectile has sufficient safety such that it will not function on heavy rain or tall grass, nor will it function if dropped on its nose from a height of 50 feet onto concrete or a steel plate. Yet, the same projectile is so sensitive that it will function when it strikes normal earth, soft wet earth, gravel, sand, as well as when it strikes hard surfaced roads and the other terrain at high angles of obliquity (graze impact).

We claim:

1. In a small arms projectile for use in a spotting rifle and in which the projectile has a metal body portion, a soft metal jacket radially enclosing the projectile for substantially its full axial length, means to reduce any tendency for relative rotation between the jacket and body portion of the projectile, an incendiary charge in a forward portion of said projectile, and an impact sensitive primer charge in front of said incendiary charge for firing the same, the combination therewith of the improvement in sensitivity of the projectile for firing the incendiary charge when the projectile strikes normal earth, soft wet earth, gravel, and sand as well as when it strikes hard surfaced roads and the like but which will not fire the incendiary charge in heavy rain, or tall grass, nor when the projectile is dropped on its nose from a height of 50 feet onto concrete or a steel plate, said improvement including an incendiary container between the jacket and incendiary charge for at least the full length of said incendiary charge, said container being tapered, contiguous to both said incendiary charge and jacket for substantially the full length of said charge and conforming to the shape of the forward portion of said jacket around said incendiary charge, said primer charge being disposed within said container and a forward end of said container being flattened and flexible but spaced from a front end of said primer charge, said jacket being extended in front of said flattened container forward end, and the walls of said jacket in front of said container forward end being tapered in thickness to a sharp edge which is substantially circular where a space is provided within said jacket and in front of said flattened container forward end for entrapment of material, and said flexible flattened container forward end being adapted for the transfer of energy through said flattened forward end for firing said primer charge.

2. A projectile according to claim 1 for a 50 caliber rifle in which the flattened container forward end is about .012 inch thick, the circular edge on said jacket in front of said container forward end is about .160 inch in diame ter, and said container is aluminum.

3. A projectile according to claim 2 in which the incendiary charge is composed of about 50% red phosphorous and about 50% by weight of barium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 1,283,158 Griflith Oct. 29, 1918 2,669,182 Weiss Feb. 16, 1954 2,764,092 Massey Sept. 25, 1956 FOREIGN PATENTS 310,766 Germany June 17, 1920 417,314 GreatBritian Oct. 2, 1934 

